Hybrid energy: the best of both worlds
Francesc Filiberto, BNZ, Spain, outlines why solar-wind hybridisation is the next step for renewable energy in Southern Europe in this article published by Energy Global.
More than 2700 years ago, the great wise man, Homer, said: “Not vain the weakest, if their force unite.” Although it is assumed that his phrase has nothing to do with the world of energy, and even less with that of renewables, this quote can still be linked to the sector. So-called ‘green’ energy sources are incredibly beneficial for the planet, but humans are only at the initial stage of the development of renewable projects; there are still many forces that need to be joined in order to achieve better power with fewer resources. In short, it is a question of efficiency and, above all, hybridisation.
This word, which is increasingly used in the world of energy, makes perfect sense when it is explained that its goal is to try to generate electricity from several renewable energy sources, mainly solar and wind, at a common connection point. This makes it possible, first of all, to optimise the connection points to the grid. Storage systems could even be included that further help to adapt production to demand and take part in adjustment services. However, this approach raises hundreds of technical questions about how to achieve perfect hybridisation.
The U.S. Department of Energy (DOE) highlights innovative opportunities to spur joint research on hybrid energy systems in its last statement ‘Hybrid Energy Systems: Opportunities for Coordinated Research’. The report, a collaborative effort among DOE and nine US laboratories, says hybrid energy systems that integrate multiple generation, storage, and energy conversion processes can play a major role in decarbonising the US economy. These systems can produce high-value commodities such as hydrogen, power industrial processes, and provide more grid flexibility to increase the deployment of renewable energy technologies.
What are the benefits? Is everything as simple as it seems? It is clear that the biggest advantage is the improvement of the load factor at the connection points, since the energy injected through the same node is increased. In addition, from the point of view of consumption, the quality and stability of the supply are improved and more stability is provided to the grid, since solar and wind energy production are relatively complementary. Observing the production curves of these two energy sources, it is clear that the peaks of each of the energies are in different bands, so this complementarity allows the connection to the grid to be optimised.
According to the Australian Renewable Energy Agency (Arena), hybrid technologies have also another benefits, such as reducing the risk for investors and ensuring immediate reliability and affordability. They can also support a smoother transition to more renewable energy generation in the future. For example, in Australia, the King Island Renewable Integration project is a world-leading power system that will supply over 65% of King Island’s energy needs using renewable energy (wind and solar), reducing the island’s carbon dioxide emissions by more than 95%. It is necessary to highlight that King Island is not connected to a mainland electricity supply.
The main objective of hybridisation has to be to unite different renewable energies in a single node so that they can cover a large part of the base load and eventually replace other technologies, such as nuclear energy, for example. This could therefore reduce the complexity of the grid and help make daily energy management simpler. In addition, hybridisation allows for savings on CAPEX and OPEX of between 10% and 15% on new renewable projects, according to the Renewable Energy Sources Producers Association (APPA).
Impact on the land
However, on the other hand, it must be taken into account that renewable energies have an obvious impact on the land due to the large amount of space required, so a project must be carefully planned and carried out in order to minimise its impact on its surroundings. The facilities must be made as environmentally integrated as possible; they cannot be designed without taking into account landscape and environmental criteria just because they produce green energy. It is a matter of studying the territory well, always considering a positive impact for all the plants that are designed.
And herein lies the greatest complexity of hybridisation: location. Wind farms are located in areas with sufficient wind resources, sometimes mountainous, while for solar plants a flatter terrain is preferable. At BNZ, it is studying projects of this type in the north of Portugal, although there are important difficulties in developing a solar plant due to the topography of the territory, which will result in a reduction of the generation capacity of this kind of energy. In any case, it is clear that both forms of production can coexist, and it is the designers’ job to strike a balance between both technologies.
In some developing countries and regions such as India, hybridisation has been a major initiative to provide full power supply to a community without access to electricity. But in these cases, the landscape and the environment take a back seat with the aim of prioritising access to electricity in the community. Also relevant is the Asian Renewable Energy Hub (AREH) project, which plans to install approximately 7.5 GW of hybrid wind energy with 3.5 GW of photovoltaic energy in Australia in 2023, with the aim of exporting 40 TWh of clean energy to Indonesia and Singapore. In Europe, however, the development of hybridisation lags behind.
Even so, there are already some pilot projects in the south of Spain, where, in addition to having a large land area to develop solar energy, there are also great options to obtain wind energy. In Cadiz, for example, the southernmost province of mainland Spain, projects were already initiated in 2018 by Vestas and EDPR. The latter company also announced the construction of the first fully commercial hybrid wind and photovoltaic plants in Spain last year. The idea was to use the solar capacity that was awarded at the time in the renewable auction to expand the capacity of four wind farms, taking advantage of the existing energy evacuation infrastructure and increasing the production and profitability of the entire facility.
Regulation is becoming increasingly favourable to this type of hybrid projects in Southern Europe. In Spain, Royal Decree 1183/2020 recognises hybrid installations as the combination of two renewable technology generation modules. In Portugal, on the other hand, legislation on this aspect will soon be introduced, and is expected to be even easier to develop. Meanwhile, in Italy, the geographical conditions of regions such as Puglia or Sicily, mean that solar and wind energy, today, already coexist on the same land.
Hybridisation with storage systems Spanish legislation does not yet regulate hybridisation with storage systems, although with respect to previous legislation, it is true that the legal vagueness that existed with regard to storage in Law 24/2013 on the Electricity Sector has been eliminated. There are other countries, such as the UK, that are studying a reduction in the load of the connection to the transport network for storage, seeking to boost their integration and favour investment in this essential technology. Also, the DOE report mentioned above outlines that in response to recent and dramatic changes to the US electric grid, the topic of hybridisation is growing in popularity within discussions related to the evolution of the US energy sector. Customer-sited systems that combine solar photovoltaics and battery technologies are being deployed for techno-economic and resilience benefits.
So why is it so important to move forward on this point? Energy hybridisation is interesting because it allows the connection point to be optimised, while the investment is the same in each solar and wind plant. But there is a problem, since with hybridisation it must be assumed that when the combined production exceeds the maximum capacity of the connection point, the surplus energy must be discarded. On the other hand, if when hybridising one or more renewable technologies, a storage technology was to be available, its efficiency would also be increased, its generation profile would be flattened and the use of the natural resource would be maximised, with it being possible to shift the generation surpluses from times of maximum resource availability and low demand to times of peak demand and low resource availability.
Some of the currently existing storage technologies are: hydraulic pumping (PHS), Li-Ion batteries, lead-based batteries, REDOX flow batteries, sulfur-sulfide batteries, flywheels, compressed air systems (CAES), zinc-air, supercapacitors and hydrogen generation, among others. Another emerging form of storage is the production of green hydrogen, which is produced by electrolysis from renewable energy. In general, the hybridisation of renewables and storage translates into a reduction in installation costs that, in the case of photovoltaics, is estimated at between 7-8%, according to APPA Renewables.
But the business model is a bit more complicated because of the cost of storage systems. There are already some pilot projects at the international level, but with low profitability. The reason is the large investment in CAPEX for the storage system, which means that the cost, also known as levelised cost of storage (LCOS) of the stored energy exceeds €100/MWh.
It is therefore necessary to optimise the production costs of storage systems to reduce their CAPEX. This is perhaps an achievable goal, shown by the extraordinary cost reduction of renewable energy production technologies in recent years.
Given this scenario with the need to lower the cost of storage systems, one of the tools that can help in this transition phase is the Next Generation EU Fund. In Spain, for example, the government proposes allocating part of the fund to the massive installation of renewable generation parks and the advancement of new storage technologies such as hydrogen. As a result, the hope is that this union between these energy sources with great potential will increasingly become a reality.
This article was published in the spring issue of Energy Global magazine.